The overall goal of these studies is to understand how the HM genes regulate immune responses. The TIM gene family, discovered by our group in 2001 using a positional cloning strategy in congenic mice, potently regulates innate and adaptive immune responses. In the previous grant period, we showed that TIM-1 is an important costimulatory molecule for T cells and an important susceptibility gene for atopic diseases, and that TIM-4 and TIM-1 function as receptors for phosphatidylserine (PtdSer). a critical marker of apoptotic cells. The current Program Project builds on these seminal findings, and consists of four interconnected and complementary Projects focusing on different aspects of TIM interactions with PtdSer expressed by apoptotic cells. The overall hypothesis is that the TIMs function as pattern recognition receptors that sense PtdSer as a DAMP (damage associated molecular pattern), and that the TIMs function either to clear apoptotic cells or to amplify immunity by responding to apoptotic/dying cells. In Project 1, we will study TIM-1 expressing natural killer T (NKT) cells, which function to sense and become activated by apoptotic cells in the liver and in the lungs. In Project 2, we will examine intracellular, molecular and functional consequences of PtdSer on apoptotic cells binding to TIM molecules on antigen presenting cells (APCs) and T cells. In Project 3 we will examine the role of TIMs in in vivo models of respiratory and oral tolerance, in which clearance of apoptotic cells by TIM expressing APCs plays a critical role. In Project 4 we will examine the structure of TIM proteins and the influence ofthe TIM gene polymorphisms on ligand recognition and presentation of ligand binding epitopes. Our Projects utilize unique reagents, including TIM specific mAbs, TIM-1 transgenic, TIM-4 transgenic and TIM-I'' and TIM-3' mice, TIM crystals, monkeys and complementary approaches involving crystallogra phy, structural biology, virology, biochemistry as well as cellular and molecular immunology, in models of asthma, hepatitis, respiratory tolerance and oral tolerance. Our studies will demonstrate that the T/Mgene family evolved to sense the presence of apoptotic cells at different phases of immunity, and to play a major role in regulating distinct compartments of mucosal immune responses by affecting cell activation, survival, death and immune tolerance. The results of these studies will greatly impact our understanding of immunity, and may lead to important new therapies for inflammatorv diseases, including asthma and food allergy. RELEVANCE (See instructions): The 7//W genes have been shown to be important disease susceptibility genes (asthma, allergy, atopic dermatitis, food allergy and rheumatoid arthritis) and to potently regulate immune responses. We believe that further study of these molecules will greatly improve our understanding of disease mechanisms, and are likely to lead to novel therapies for asthma and food allergy.